Radiation choke



July 21, 1959 M. w. SCHELDORF 2,396,206

RADIATION CHOKE Filed Nov. 8, 1955 3 Sheets-Sheet l l' C I w/mezkwzkzz /y WW-11% s7 July 21, 1959 M. w. SCHELDORF 2,896,205

' RADIATION CHOKE Filed Nov. 8, 1955 5 Sheets-Sheet 2 0 4o 50 I20 I60 200 2% 280 320 sec ANGLE L I Z; 25

July 21, 1959 Filed Nov. 8, 1955 M. W. SCHELDORF RADIATION CHOKE .3 Sheets-Sheet 3 ANGLE 200 2 4'0 28 320 360 fiflwfisr WWW/hick 6412 07/9 United RADIATION CHOKE Marvel W. Scheldorf, Palos Heights, 111., assignor to Andrew Corporation, a corporation of Illinois The present invention relates to a radiation choke, and

v more particularly to a compact choke which is to be applied to a radiating conductor. I

In my co-pending patent application, Serial No. 527,842 filed August 11, 1955, now U S. Patent 2,852,- 774, for a Suppressor-Type Antenna, there was shown an application of a radiation choke to an antenna to isolate .one portion of the antenna structure from the adjacent portion which was supposed to be the efiective radiator. In my co-pending patent application, Serial No. 540,239 filed October 13, 1955 for a Radiation Choke, there was shown one type of choke and the detailed principles of construction thereof.

In some instances the radiation choke shown in the above mentioned co-pending application may be deemed to be unsuitable because of the long dimensions thereof. Where space must be conserved, it is proposed to use a different type of radiation choke which will serve to isolate radiation along a conductor or to isolate a portion of a conductor so that its effect on adjacent elements is eliminated.

It is an object of the present invention to provide a new and improved radiation choke.

Other and further objects of the present invention subsequently will become apparent by reference to the following description taken in conjunction with the accom panying drawings, wherein:

Figure 1 is a longitudinal cross-section view showing the constructional details of the choke comprising the present invention;

Figure 2 is an end view as seen in the direction of the arrows along the line 22 of Figure 1;

Figure 3 is a cross-sectional view as seen in the direc tion of the arrows along the line 3--3 of Figure 1;

Figure 4 is a diagrammatic representation of an antenna structure;

Figure 5 is an E-plane radiation pattern of the antenna shown in Figure 4;

Figure 6 is a diagrammatic representation of an antenna structure similar to that shown in Figure 4, to which chokes of the present invention have been applied to illustrate their effectiveness; and

Figure 7 is an E-plane radiation pattern of the antenna shown in Figure 6.

Referring to Figures 1, 2 and 3 there is shown a compact radiation choke mounted on a central conductor 11. The choke has an outer cylindrical member 12 which has a physical length of one-quarter wavelength. At the middle of the cylinder 12 there is a conductive annular ring 13 which is fastened to the conductor 11 by suitable means, such as a set screw 14. The ring 13 is also secured to the outer cylinder 12 by suitable fastening means, such as a cap screw 15. On either side of the central annular member 13 are a plurality of annular insulating discs 16 which abut the central member 13 and on the other sides abut cylindrical sleeves 17 surrounding the central conductor 11. Beyond the cylindrical sleeves 17 are a plurality of insulating discs 18 which are retained r tes Patent 0 in position by suitable snap rings 19 located adjacent the ends of the cylindrical member 12 on the inner conductor 11. The insulating discs 16 and 18 are so selected and spaced within the outer cylinder 12 so as to provide sufiicient dielectric to produce a relative wavelength velocity of fifty percent. Thus, in effect, while the outer cylinder 12 is one-quarter wavelength long, it has an electrical length of one-half wavelength, which provides the necessary high magnitude of terminal impedances.

In order to illustrate the operation of the present invention there has been shown an antenna structure comprising a radiating conductor 21 which is three wavelengths long. At the center a dipole structure one-half wavelength long, indicated as 22, is arranged to be connected to a transmission line. The dipole 22 is spaced from the radiating conductor 21 .05 wavelengths. The resultant structure, therefore, represents a folded dipole antenna which has extended secondary arms formed by the extensions of the conductor 21. This then would represent certain installations where a folded dipole might be connected to or closely adjacent to some conductor or metallic reflecting or radiating structure. The E-plane radiation pattern shown in Figure 5 clearly illustrates the unsatisfactory pattern obtained from an antenna such as that shown in Figure 4.' I

It may now be assumed that the same type of structure shown in Figure 4 is utilized in'Figure 6, and closely adjacent to the central folded dipole structure, on either side thereof, there have been placed radiation chokes 23 each of a construction similar to that shown in Figure 1. This then will produce an efiect illustrated by the E-plane radiation pattern characteristic illustrated by the curve in Figure 7. A comparison of the curves of Figure 5 and Figure 7 will readily be appreciated by those skilled in the art as clearly illustrating the usefulness and efiecitveness of the radiation choke comprising the present invention.

While for the purpose of illustrating and describing the invention a specific embodiment has been shown in the drawings, it is to be understood that such variations are contemplated as may be commensurate with the spirit and scope of the appended claims.

I claim as my invention:

1. A radiation choke arranged to be mounted on a central radiating conductor to isolate longitudinal portions of the conductor for signals of a given frequency comprising a cylindrical section coaxial to the central conductor and of a length less than one-half the freespace Wavelength of such signals, a conductive annular member interconnecting the cylindrical section at its center with the coaxial radiating conductor, said annular member being otherwise unconnected, and dielectric members positioned within said cylindrical section in an amount sufiicient to provide a reduced velocity of propagation of radiant high frequency energy such that the choke has an internal electrical length of one-half wavelength.

2. A radiation choke assembly comprising a central radiation conductor, a coaxial cylindrical section appreciably less than one-half wavelength long, a conductive disc interconnecting said radiation conductor with the middle of said cylindrical section, the cylindrical section being otherwise unconnected, and insulating material interposed between said conductor and said cylindrical section on both sides of said conductive disc in an amount sufficient to make the effective internal electrical length of said choke one-half wavelength long.

3. A radiation choke assembly comprising a central conductor, a coaxial cylindrical section one-quarter wavelength long, a conductive disc interconnecting said conductor with the middle of said cylindrical section, the cylindrical section being otherwise unconnected, and in- "P tented Ju 1 1 5 sulating material interposed at spaced longitudinal intervals between said conductor and said cylindrical section on both sides of said conductive disc in an amount sufiicient to make the effective internal electrical length of said choke one-half wavelength long.. w

4. A radiation choke assembly comprising a central conductor, a coaxial cylindrical section one-quarter wavelength long, a conductive disc interconnecting said conductor with the middle of said cylindrical section, said cylindrical section being otherwise unconnected, and a plurality of discs of insulating material interposed at spaced longitudinal intervals between said conductor and said cylindrical section on both sides of said conductive disc in an amount sufiicient to reduce the propagation velocity therein by one-half to make the eflective internal electrical length of said choke one-half wavelength long.

5. A radiation chokeeassembly comprising a central conductor, a coaxial cylinder surrounding said conductor and being one-fourth wavelength long, said cylinder being otherwise'unconnected, a conductive disc interconnecting the middle of said cylinder with said conductor, and a plurality of discs of insulating material interposed at spaced longitudinal intervals between said cylinder and said conductor in an amount suflicient to reduce the velocity of transmission of high frequency energy by one- 25 half.

6. A radiation choke assembly for isolation of a portion of an antenna structure from signals of a particular frequency comprising an elongated antenna element, an

electrically conductive enclosure etfectively surrounding a longitudinal portion of the antenna of one-quarter wavelength at said frequency, a conductive connection between the element and the enclosure at the longitudinal center thereof, the enclosure being otherwise unconnected, and a dielectric in the enclosure and surrounding the element in an amount sufficient to reduce the velocity of propagation within the enclosure by one-half.

7. A radiation choke assembly for isolation of portions of an antenna structure from signals of a particular frequency comprising an elongated antenna element, an electrically conductive enclosure effectively surrounding a longitudinal portion of the antenna of less than onehalf wavelength at said frequency, a conductive connection between the element and the enclosure at the longitudinal center thereof, said enclosure being otherwise unconnected, and a dielectric in the enclosure and surrounding the element in an amount sufiicient to reduce the velocity ofepropagation within the enclosure to a value such that the internal electrical length of the enclosure is a half-wavelength.

References Cited in the file of this patent UNITED STATES PATENTS 2,113,136 Hansell et a1. Apr. 5, 1938 2,428,001 Tubbs Sept. 23, 1947 FOREIGN PATENTS 573,436 Great Britain Nov. 21, 1945 

